Improving weld penetration by two-TIG arc activated via mixing oxygen into shielding gas

In order to improve welding efficiency of conventional TIG welding process, a new activating TIG (A-TIG) welding process, named activating arc two-TIG (AT-TIG) welding, was developed by using two-TIG arc activated via mixing minor oxygen into the shielding gas of the front welding torch. The effect of the oxygen flow rate, welding current carried by two tungsten electrodes, and welding speed on the weld formation were investigated for the bead-on-plate welding of SUS304 stainless steel. It was found that, compared to conventional TIG welding, this method can successfully obtain a markedly deepened weld penetration, even at a relatively higher welding speed. Mixing of O₂ into the argon shielding gas do not have a significant effect on the microstructure of the weld metal. The dramatically improved weld depth can be achieved at a lower oxygen flow rate and the corresponding impact toughness energy of the weld reaches as much as 92.3% of the workpiece. In addition, the modulation of the current proportions for each welding torch plays a prominent role in the weld formation, which was accounted by a numerical model that the current apportionment for each electrode results in the change of the arc plasma flow and thus the oxygen transfer process from the arc plasma to the weld pool. The predominant effect of the oxygen on the formation of the weld pool shape and the weld formation was demonstrated by a weld-bead-shift experiment. Therefore, the oxygen transfer process from the arc plasma to the weld pool and the mechanisms for enhancing the weld penetration in this welding process were clarified.